This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-368501 filed on Dec. 4, 2000, No. 2000-382519 filed on Dec. 15, 2000, No. 2001-339553 filed on Nov. 5, 2001, and No. 2001-348534 filed on Nov. 14, 2001.
1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine provided with a variable valve timing mechanism.
2. Related Art
In recent years, there has been developed a technology for activating a catalyst at an early time after an internal combustion engine is started to meet requirements according to an emission regulation. In accordance with this technology, in order to activate a thee-way catalyst at an early time, the temperature of the catalyst is increased at an early time by deliberately exhausting incompletely combusted fuel by retarding an ignition angle (crankshaft angle corresponding to ignition timing).
A technology to increase the temperature of a three-way catalyst at an early time is disclosed in JP-A-6-117348. In order to warm up a three-way catalyst in accordance with this disclosed technology, retard angle control of an ignition timing is executed. Control is also executed to open an intake valve during a period in which a piston in the internal combustion engine moves from the top dead center to the bottom dead center in a transition from a gas exhaust stroke to a gas intake stroke. By executing such ignition angle retard control, the speed of combustion is reduced. Thus, if the intake valve is opened with a normal timing, combusted gas will flow in the reverse direction into the intake passage. It is therefore likely that a backfire occurs. By executing the control of the intake valve, however, the combusted gas can be prevented from flowing in the reverse direction into the intake passage. As a result, a backfire phenomenon can be prevented from occurring during the control of the ignition angle retarding.
In addition, as control executed at a start of the internal combustion engine, there is known control to correct a fuel injection volume at the start of the engine by increasing the volume in order to start the engine with a high degree of reliability. One reason to correct the fuel injection volume is that, at a cold start of the internal combustion engine, a low temperature of the engine affects the degree of evaporation of the fuel. Specifically, the lower the temperature of water, the more difficult it is for the fuel to evaporate. That is, some of fuel injected by an injector unavoidably sticks on the intake passage and/or the intake valve. Since a large amount of fuel is stuck on the intake passage and/or the intake valve at a low temperature of the internal combustion engine, it is necessary to correct the fuel injection volume by increasing the fuel injection volume.
If a large amount of fuel is stuck on the intake passage and/or the intake valve, some of the stuck fuel is difficult to remove. Therefore the volume of fuel flowing into the combustion chamber tends to vary. As a result, combustion of fuel also becomes unstable and control of an air-fuel ratio becomes difficult to execute as well.
It is thus a first object of the present invention to provide a variable valve timing apparatus capable of providing stable combustion of fuel even if the control of an ignition angle retarding is executed.
In order to achieve the first object of the present invention, there is provided an internal combustion engine executing ignition angle retarding control of an ignition timing in order to warm up a catalyst at an early time, wherein, at a cold start of the engine, a timing to open an intake valve is set at a retard angle and control of fuel injection is executed in accordance with a timing to open the intake valve at a retard angle.
By setting the timing to open an intake valve at a retard angle, a closed state of the intake valve is sustained even after a piston of the internal combustion engine passes the top dead center, moving toward the bottom dead center. As a result, a pressure in a combustion chamber is relatively low in comparison with a pressure in an intake passage. In this state, the intake valve is opened so that the flow velocity of gas increases due to the difference between the pressure in the combustion chamber and the pressure in the intake passage. When the intake valve starts to open, the flow velocity of the gas increases in particular. This is because intake air flows into the combustion chamber through a small area. Thus, by controlling injection of fuel so as to take in the fuel to the combustion chamber with this timing, atomization of the fuel is promoted to result in good combustion. In addition, since this control is executed at a cold start, the amount of fuel stuck on the intake passage can be reduced due to the increased flow velocity of the fuel. With the reduced amount of fuel stuck on the intake passage, the amount of exhausted gas such as an HC gas also decreases as well.
It is a second object of the present invention to provide a control apparatus for an internal combustion engine capable of executing stable control of an air-fuel ratio by reducing a correction quantity for increasing a fuel volume and the amount of fuel stuck on the intake passage.
In order to achieve the second object of the present invention, a timing to open an intake valve and/or a lift quantity are adjusted to increase the flow velocity of fuel. The fuel injection volume is corrected to reduce the amount of fuel stuck on the intake system on the basis of the timing to open the intake valve and/or the adjusted lift quantity.